The invention related to an active suspension system for motor vehicles or the like with actual-value pick-ups assigned to the wheels, which pick-ups generate in each case a signal representing the distance between vehicle body and wheel and feed it to a computer, as well as with spring and support assemblies which are assigned to the wheels, are controlled by the computer and whose supporting forces and/or resistances counteracting the lifting movements of the wheels are influenced by the computer in a predeterminable way.
In the case of conventional passive suspension systems, the value of the supporting forces depends in each case only on the lifting position of the wheels, i.e. the supporting force generated by a spring assembly increases with decreasing distance between the respective wheel and the body of the vehicle.
In spite of the high level of development of passive suspension systems, it remains unavoidable that compromises have to be made in setting. If, for example, the suspension is to be set soft with a view to high comfort, when traveling around a bend at high speed, the vehicle body will incline comparatively strongly towards the outside of the bend. Consequently, relatively great roll angles occur when traveling around a bend.
There is the possibility of reducing the roll angles by arrangement of stabilizers which, when there is compression of a wheel, try to urge the corresponding wheel on the other side of the vehicle likewise in the direction of compression, so that the spring assemblies on the inside of the bend are also used for supporting the wheels on the outside of the bend. However such stabilizers impair the suspension comfort if the vehicle travels over unevenesses in the ground only with the wheels of one side of the vehicle or if undulations in the ground running obliquely to the direction of travel are passed over.
Similar problems also occur with active suspension systems.
An active suspension system of the type specified at the beginning is known from German published Application (Offenlegungsschrift) 3,212,433 in which signals, which are dependent on the lifting positions of the wheels or of the assigned support assemblies and which change progressively with increasing deviation of the lifting position from an initial position or position of rest, are generated by means of sensors. These signals are then compared by means of a computer, the computer determining in each case which support assembly or wheel deviates the furthest from the initial position or position of rest. Then, the support assembly assigned to this wheel is actuated in the sense of a change in the respective supporting force.
German published Application (Offenlegungsschrift) 3,101,194 shows an active suspension system, in which first of all signals which reproduce the vertical accelerations of individual wheel groups are generated. From these signals, it is determined the extent to which the assigned support assemblies are to be deflected. Thereafter, the support assemblies are actuated in such a way that the deflection of the same measured in each case approximates to the deflection to be aimed for.
A suspension system in which essentially only the intensity of the damping of the suspension strokes is influenced actively is shown from German published Application (Offenlegungsschrift) 2,441,172. For this purpose, signals which represent the lifting position of the support assemblies assigned to the wheels and the vertical accelerations of the vehicle with the corresponding support assemblies are generated by means of corresponding sensors. Then the damping of the suspension system is varied in such a way that the accelerations of the vehicle body approximate a set value, which depends on the lifting position of the support assemblies.
An object of the invention is now to create an active suspension system which allows optimum setting in a particularly simple way.
This object is achieved according to the invention with a suspension system of the type specified above by the compute determining in each case from the pick-up signals an actual value of the averaged ground clearance, an actual value of the averaged roll angle and an actual value of the averaged pitch angle and actuating the spring and support assemblies as a function of the deviations of these actual values from predetermined or predeterminable set values.
The invention is based on the general idea that each movement of the vehicle body represents a combination of a pure lifting movement relative to a reference plane as well as a rotation about the vehicle longitudinal axis (rolling movement) and a rotation about the vehicle transverse axis (pitching movement). According to the invention, these movement components are now analyzed separately, as a result of which the possibility is offered of actuating the support or spring assemblies differently when there are changes in the lifting positions of the wheels, depending on whether the change in wheel position was effected by a rolling or pitching movement or a pure lifting movement of the body or by different combinations of these movement components. As a result, at the same time the possibility is offered of countercontrolling differently when there are different types of movement of the vehicle body by means of the spring or support assemblies. In particular, it is possible for example to absorb lifting movements of the vehicle body comparatively softly to achieve good comfort, while rolling and pitching movements are substantially counteracted with a view to safe vehicle handling. Thus, it can be readily achieved that, when traveling around a bend, the vehicle only inclines a little towards the outside of the bend in spite of a soft setting of the suspension with respect to lifting movements.
Since pitching and rolling movements of the vehicle can be prevented to the greatest extent, only small pitch and roll angles occur, i.e. the spring deflection of a wheel available in each case is scarcely impaired by inclined positions of the vehicle body with respect to the plane of the carriageway. Consequently, the possibility is offered of setting the suspension very comfortably with respect to lifting movements, because there is a large spring deflection available even in such driving conditions which would lead to larger pitch or roll angles in the case of conventional vehicles. Furthermore, the advantage is achieved that the wheel suspensions execute virtually only movements close to their optimum position and thus no self-steering of the vehicle, caused by the compression kinematics, can occur.
In addition, the forces necessary for the damping or suppression of rolling movements of the vehicle can be generated in predeterminable proportions by the support assemblies of the front and rear wheels in order to set the control tendency of the vehicle, for example to under-controlling or over-controlling or to neutral behavior.
Accordingly, a particularly safe and well controllable vehicle handling can be expected even in extreme situations.
The mean value of the distances of all wheels with respect to the vehicle body, or a value correlated with it, may be expediently used as averaged ground clearance. The difference between the mean value of the distances of the front wheels from the vehicle body and the mean value of the distances of the rear wheels from the vehicle body, or a value correlated with this difference, may serve as averaged pitch angle. The difference between the mean value of the distances of the right wheels from the vehicle body and the mean value of the distances of the left wheels from the vehicle body, or a value correlated with this difference, are suitable as averaged roll angle. If the mean values listed above are used, the position of the vehicle is determined relative to a reference plane which is parallel to two straight lines, one of which passes through the wheel contact areas of the right front wheel and of the left rear wheel and the other of which passes through the wheel contact areas of the left front wheel and of the right rear wheel.
According to a preferred embodiment of the invention, it is provided that the actuating signals for the spring and support assemblies, and the correction of the supporting forces and/or resistances with respect to lifting movements of the wheels, effected by the actuating signals, have in each case a value which corresponds essentially to the sum of those values which the computer would calculate for a correction of the ground clearance alone, a correction of the pitch angle alone, and a correction of the roll angle alone. In this way, different types of movement of the vehicle body can be influenced separately from one another in a simple way in terms of technical control.
In cases of extreme situations, the actuating force actually set at the spring and support assembly may deviate from the calculated value. Such a situation occurs above all whenever the supporting force calculated is close to or above the maximally generated supporting force. In such extreme cases, under certain circumstances the suspension may bottom. To avoid damage in such cases, compliant stops are arranged for wheel guide elements, as in the can of conventional suspension systems.
Furthermore, in the case of the suspension system according to the invention, it is advantageously envisaged to have the computer in each case determine from the pick-up signals the variation over time of the actual values of the averaged ground clearance, of the averaged pitch angle and of the averaged roll angle and to actuate the spring and support assemblies also as a function of the rate of change of the said actual values. Consequently, the supporting forces in each case set at the spring and support assemblies depend on the one hand on the type of movement of the vehicle body, i.e. on whether the vehicle body executes lifting movements, pitching movements and/or rolling movements. On the other hand, it is also taken into consideration at what rate these movements take place.
In principle, the wheels may execute lifting movements which do not lead to a change in the mean value of the ground clearance and/or of the mean value of the pitch angle and/or of the mean value of the roll angle. If, for example, the right front wheel and the left rear wheel compress simultaneously by the same spring deflections and the left front wheel and the right rear wheel rebound simultaneously by corresponding spring deflections, the said mean values remain unchanged if they are determined in the way specified above. In order to prevent the possibility of such wheel movements being induced over a prolonged time, it is sufficient if the suspension system according to the invention always operates in the sense of a weak fundamental damping of suspension strokes.
Instead, it is also possible that the computer determines the wheel movements not influencing the said mean values from the pick-up signals and only actuates the spring and support assemblies in the sense of a damping of these movements when such movements occur.
If appropriate, the vehicle may have body acceleration pick-ups and/or wheel acceleration pick-ups in order to be able to adapt the suspension system according to the invention even better to changing driving conditions. As a result, the possibility is created in particular of reacting at an early time to accelerations or decelerations of the vehicle or to commencing travel around a bend, before the vehicle body tries to execute major pitching or rolling movements. By means of the said acceleration pick-ups, there is namely the possibility of changing the set values for the supporting forces of the spring and support assemblies at a very early time, before the vehicle body can execute major movements upon braking, accelerating or turning of the steering. Those forces of inertia which try to generate the pitching and rolling movements can thus be compensated for immediately by corresponding counterforces, so that rolling and pitching movements can virtually not occur at all in the first place.
In this way, a "hard" spring characteristic can be attained particularly effectively for the pitching and rolling movements of the vehicle body, while preserving a "soft" compression movement, beneficial in terms of comfort, of the individual wheels.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.